There are two main types of solid rocket propellants in present use, the double base type and the composite type. Because of serious and long standing problems involving the brittleness of double based propellants under low temperature conditions and their detonation characteristics, composite type propellants are favored for use in large rockets and rocket boosters.
Composite type propellants generally contain an inorganic oxidant and a fuel component incorporated into an elastomeric-type binder which is capable of being successfully cast and cured, in situ, while bonded to the inside of a rocket or booster casing. A high degree of reliability and precision in the geometry of the cast is necessary.
Because of their high burn rate, thermal stability plus high loading potential with conventional binders and plasticizers, inorganic perchlorate salt(s) such as ammonium perchlorate have been widely used as major oxidant components in many composite formulations. Such use, however, presents a serious problem due to the fact that the corresponding rocket exhaust includes a very high percentage (21%-22%) of hydrogen chloride, which constitutes both a health hazard and a serious environmental pollutant, particularly in higher atmospheric zones where convection is minimal or essentially non-existent.
As a result, continuing attempts are being made (ref Cahill et al U.S. Pat. No. 3,445,304 and Frosch et al U.S. Pat. No. 4,158,583) to wholly or partly substitute nitrate-based non-chlorine-containing salts in place of perchlorate salts as a primary oxidizer component. Such attempts have not been successful, thus far, (a) because of low or limited solids loading (b) difficulty in casting and curing the combined formulation, (a) a low burn rate with low combustion efficiency, and (d) potential thermal instability due to a rapid depletion of conventional stabilizers under moderate heat in the presence of various burn rate catalysts and metal fuel components.
It is an object of the present invention to obtain a solid propellant which does not evolve substantial amounts of hydrogen chloride in the firing exhaust.
It is a further object to obtain a stable, chlorine-free high-energy modified double based propellant composition of suitable burn rate and efficiency, which utilizes an inorganic nitrate salt as a major oxidizer component.